Event-related brain potentials (ERPs) are derived from electroencephalographic (EEG) recordings that are time-locked to a stimulus event and represent the brain's ‘on-line’ response during sensory and cognitive processing (Luck and Girelli, 1998). Prior work has shown that neuropsychological tests can be adapted for computer presentation and simultaneous ERP recordings (Connolly and D'Arcy, 2000; Connolly et al., 2000). One of the main applications of this approach involves the use of ERPs to assess patients with apparent language deficits secondary to brain injury. For example, the ability to evaluate accurately whether or not a patient can understand speech is critical to determining the type of therapeutic intervention that will most benefit the patient. Unfortunately, behavioral and/or communicative limitations following neurological damage can render the assessment of comprehension abilities difficult or even impossible. Therefore, the combination of an often used and widely accepted assessment method such as neuropsychological testing with the relatively new ability to record subtle cognitive activity using ERP techniques offers a major advantage in the assessment of aphasic patient populations. Left hemisphere stroke patients represent one group for which this situation occurs frequently because of deficits in both motor and language functions, thus limiting the efficacy of behavioral assessment methods (Enderby and Philipp, 1986; Enderby et al., 1987; Marquardsen, 1969; Morse and Montgomery, 1992; Pedersen et al., 1995; Wade et al., 1986). In these cases, ERPs can be used to evaluate the patient's language functions (Byrne et al., 1995; Connolly et al., 1999). Currently, the analysis and interpretation of the ERPs rests on predicted differences in the waveforms that result from well-known components (e.g., P300 and N400).
However, the analysis of the component differences in ERP waveforms would benefit greatly from a quantification procedure that allows for a direct comparison to traditional neuropsychological scores. When attempting to link quantitatively ERP and standardized neuropsychological measures there are at least two considerations that must be made. First, care must be taken to maintain the neuropsychological test properties during computer adaptation. Second, the presence or absence of the cognitive function under investigation must be determined by the existence of a predicted ERP component, which has been shown previously to reflect that function. In addition, selecting a test with graded levels of difficulty and sampling a population with varying degrees of deficits are helpful to characterize better the relationship between ERP and neuropsychological measures.
An excellent candidate that meets the criteria discussed above is the Peabody Picture Vocabulary Test—Revised (PPVT-R; Dunn and Dunn, 1981). The PPVT-R is a well-known test of vocabulary knowledge that involves matching a picture to a spoken word. Previous studies have shown that the PPVT-R can be adapted successfully for computer presentation and simultaneous ERP recording while maintaining the psychometric properties of the original test (Connolly et al., 1995). Moreover, the PMN (phonological mismatch negativity) and N400 components are elicited to the incongruent (or mismatching) spoken word stimuli in the computerized PPVT-R (Byrne et al., 1995a,b; Connolly et al., 1995). The PMN is an early negativity (˜275 ms) that is associated with phonological processing in speech perception (Connolly and Phillips, 1994; Connolly et al., 2001). The N400 is a well-defined negative-going waveform (˜400 ms) that is linked to semantic analysis in both speech processing and reading (Connolly and Phillips, 1994; Connolly et al., 1995; Holcomb and Neville, 1990; Kutas, 1997; Kutas and Van Petten, 1994).
The following references may be relevant to this invention:
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